Heating blanket

ABSTRACT

An electric heating blanket including a flexible sheet-like heating element and a shell. The shell covers the heating blanket an includes two sheets of flexible material welded together.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. § 119(e) to co-pendingU.S. provisional application 60/895,736, filed Mar. 19, 2007, which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention is related to heating or warming blankets or padsand more particularly to those including electrical heating elements.

BACKGROUND

It is well established that surgical patients under anesthesia becomepoikilothermic. This means that the patients lose their ability tocontrol their body temperature and will take on or lose heat dependingon the temperature of the environment. Since modern operating rooms areall air conditioned to a relatively low temperature for surgeon comfort,the majority of patients undergoing general anesthesia will lose heatand become clinically hypothermic if not warmed.

Over the past 15 years, forced-air warming (FAW) has become the“standard of care” for preventing and treating the hypothermia caused byanesthesia and surgery. FAW consists of a large heater/blower attachedby a hose to an inflatable air blanket. The warm air is distributed overthe patient within the chambers of the blanket and then is exhaustedonto the patient through holes in the bottom surface of the blanket.

Although FAW is clinically effective, it suffers from several problemsincluding: a relatively high price; air blowing in the operating room,which can be noisy and can potentially contaminate the surgical field;and bulkiness, which, at times, may obscure the view of the surgeon.Moreover, the low specific heat of air and the rapid loss of heat fromair require that the temperature of the air, as it leaves the hose, bedangerously high—in some products as high as 45° C. This posessignificant dangers for the patient. Second and third degree burns haveoccurred both because of contact between the hose and the patient'sskin, and by blowing hot air directly from the hose onto the skinwithout connecting a blanket to the hose. This condition is commonenough to have its own name—“hosing.” The manufacturers of forced airwarming equipment actively warn their users against hosing and the risksit poses to the patient.

To overcome the aforementioned problems with FAW, several companies havedeveloped electric warming blankets. Some of these warming blanketsemploy flexible heaters, the flexibility of which is desirable tomaintain when employing the blankets. In many cases, an electric warmingblanket employs a shell for holding the heater and for serving otherpurposes. For example, in some cases the shell includes layers formed ofa substantially water impermeable material to help prevent fluid damageto the heater. Also, when these heaters are used for patient or othercare, especially in the operating room, the shell can protect thepatient and others in the vicinity from electric shock hazards. Inaddition to often providing a seal around the heater, the shell oftencontains a fastening mechanism that must reliably attach the heater tothe shell to prevent electrical shorting across the heater duringfolding of the electric warming blanket.

Because the seals of the shell must be very reliable, the seals havetraditionally been adhesive seals that are reinforced with combinationsof sewing, rivets, and grommets. Sewing stitches, rivets, and grommetsall share one characteristic—they all perforate the material layers tocreate a mechanical linkage between the layers.

While such a reinforced bond may be desirable for strength, it cancreate additional problems when used during surgery or medicalprocedures. For example, heated blankets placed over a patient during asurgery or medical procedure are frequently soiled with waste blood orother body fluids. The fluid waste can saturate the stitching and thendry and accumulate in the thread or the stitch holes. If rivets orgrommets are used for reinforcement, additional crevasses are introducedthat can trap waste fluids. When the outer shell of the blanket iscleaned by hospital personnel, it is nearly impossible to clean theresidual contaminating materials out of the holes, crevasses, and/orstitches. Therefore, the stitching holes and thread, the grommets,rivets and snaps can all become sources of microbial contaminationbecause they can not be thoroughly cleaned and disinfected.

Accordingly, there remains a need for heated blankets and shells forflexible heaters that is readily and thoroughly cleanable. Variousembodiments of the invention described herein solve one or more of theproblems discussed above in addition to other problems that will becomeapparent.

SUMMARY

Certain embodiments of the invention include an electric heating blanketincluding a flexible sheet-like heating element and a shell. The shellcovers the heating blanket an includes two sheets of flexible materialwelded together. In some embodiments the weld couples the sheetstogether about the edges of the heating element. In some embodiments,the weld couples the sheets about the edges of the sheets.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments of thepresent invention and therefore do not limit the scope of the invention.The drawings are not to scale (unless so stated) and are intended foruse in conjunction with the explanations in the following detaileddescription. Embodiments of the present invention will hereinafter bedescribed in conjunction with the appended drawings, wherein likenumerals denote like elements.

FIG. 1 is a top plan view of a heating blanket, according to someembodiments of the present invention.

FIG. 2A is a plan view of a flexible heating blanket subassembly for aheating blanket, according to some embodiments of the present invention.

FIG. 2B is an end view of some embodiments of the subassembly shown inFIG. 2A.

FIG. 3A is a top plan view of a heating element assembly, according tosome embodiments of the present invention, which may be incorporated inthe blanket shown in FIG. 1.

FIG. 3B is a section view of the temperature sensor assembly of FIG. 3A.

FIG. 4A is a top plan view of a heating element assembly, which may beincorporated in the blanket shown in FIG. 1.

FIG. 4B is a cross-section view through section line 4B-4B of FIG. 4A.

FIG. 5A is a cross-section of a shell containing a heating elementaccording to some embodiments of the present invention.

FIG. 5B is a top plan view of the shell of FIG. 5A.

FIG. 6 is a cross-section of a shell containing an air pocket accordingto some embodiments of the present invention.

FIG. 7A is a top plan view of a shell having straps according to someembodiments of the present invention.

FIG. 7B is a cross-section of the shell of FIG. 7A.

FIG. 8 is a cross-section of a shell containing a heating elementsecured to the shell according to some embodiments of the presentinvention.

FIG. 9A is a top plan view of a shell containing reinforced hangerpoints according to some embodiments of the present invention.

FIG. 9B is a cross-section of the shell of FIG. 9A.

FIG. 10A is a cross-section of a shell containing a heating element,including an attachment point secured to the shell according to someembodiments of the present invention.

FIG. 10B is a cross-section of a shell containing a heating element,including an attachment point secured to the shell according to someembodiments of the present invention.

FIG. 11 is a cross-section of two ends of a shell containing a heatingelement, including a securing magnet.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is notintended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the following description providespractical illustrations for implementing exemplary embodiments of thepresent invention. Examples of constructions, materials, dimensions, andmanufacturing processes are provided for selected elements, and allother elements employ that which is known to those of skill in the fieldof the invention. Those skilled in the art will recognize that many ofthe examples provided have suitable alternatives that can be utilized.The term ‘blanket’, used to describe embodiments of the presentinvention, may be considered to encompass heating blankets and pads.

FIG. 1 shows a heating blanket 100 according to some embodiments of thepresent invention. As shown, the heating blanket 100 is generallyrectangular. Embodiments of the present invention can be used inconnection with a wide variety of heating blankets. For example, in somecases, the heating blanket can be a blanket sized and shaped for theupper body or upper body limb (e.g., a wrap-around blanket), or ablanket sized and shaped for the lower body or lower body limb. In somecases the heating blanket can be used in conjunction with a disposablecover.

The heating blanket 100 of FIG. 1 includes a shell 105 that can bedurable and waterproof. As shown, a portion of the shell 105 is cutaway, revealing a heating element assembly 350. The heating elementassembly 350 is generally covered by the shell and can extend within theshell 105 between edge 112 and edge 114 and between edge 116 and edge118. An electrical connector housing 325 and a corresponding connectorplug 323 can be coupled to the shell 105, thereby enabling access to atemperature sensor assembly such as those discussed below.

The shell 105 can protect and isolate the heating element assembly 350from an external environment of heating blanket 100. The shell 105 caninclude a water-resistant material layer that can form a substantiallyhermetic seal around the heating element assembly 350. The shell 105 canprovide further protection to a patient disposed beneath heating blanket100 against electrical shock hazards. According to preferred embodimentsof the present invention, shell 105 is waterproof to prevent fluids(e.g., bodily fluids, IV fluids, cleaning fluids, etc.) from contactingthe heating element assembly 350. In some preferred embodiments, shell105 may further include an anti-microbial element (e.g., a SILVERion™antimicrobial fabric available from Domestic Fabrics Corporation orUltra-Fresh™ from Thomson Research Associates).

According to an illustrative embodiment of the present invention, shell105 comprises a nylon fabric having an overlay of polyurethane coatingto provide waterproofing. The coating can be on at least an innersurface of each of the two sheets, further facilitating a heat sealbetween the two sheets, according to preferred embodiments. In otherembodiments, the shell 105 comprises polyvinyl chloride (PVC) tofacilitate an RF weld to bond the sheets. It should be noted that,according to some embodiments of the present invention, a covering forheating element assemblies may be removable and, thus, include areversible closure facilitating removal of a heating element assembly350 therefrom and insertion of the same or another heating elementassembly 350 therein. In some embodiments, shell 105 comprises a PVCfilm of sufficient thickness to provide the necessary strength. In somesuch embodiments, the edge seals can be softer.

In some embodiments, one or more layers may be positioned between theheating element assembly 350 and the shell 105. For example, in someembodiments, a layer of thermally insulating material (e.g., polymericfoam or high-loft fibrous non-woven material) can be included in one ormore locations. In some instances, a layer of thermally insulatingmaterial can be positioned to protect a portion of the patient from theheating element assembly 350 in the event that part of the shell 105 isinadvertently placed under that portion of the patient. In suchinstances, a layer of thermal insulating material can be positionedbetween the heating element assembly 350 and the patient-contactingsurface of the shell 105. In this way, in the event that part of theshell 105 is inadvertently placed under that portion of the patient,that portion of the patient can contact an insulated portion of theshell 105 rather than a non-insulated portion of the shell 105.

In some instances a layer of thermally insulating material can bepositioned to make sure that a maximal amount of heat being generated bythe heating element assembly 350 is transferred to the patient. In suchinstances, a layer of thermally insulating material can help insulatethe heating element assembly 350 from the environment and provide a moreuniform temperature distribution. The layer of thermally insulatingmaterial can be positioned between the heating element assembly 350 andthe surface of the shell 105 that does not contact the patient. In thisway, a maximal amount of heat being generated by the heating elementassembly 350 can be transferred to the patient and not to thesurrounding environment.

In some instances a layer of thermally insulating material can bepositioned to prevent caregivers from experiencing unwanted contact withactivated heating blankets. Other layers (e.g., an electricallyinsulating layer similar to those discussed elsewhere herein) can bepositioned between the heating element assembly 350 and the shell 105.

FIGS. 2A-2B show an illustrative heating blanket subassembly 300 thatcan be incorporated into heating element assemblies (e.g., heatingelement assembly 350 of FIG. 1) in some embodiments of the presentinvention. Referring again to FIGS. 2A-2B, in many embodiments, theheating blanket subassembly 300 is flexible. The heating blanketsubassembly 300 can include a flexible sheet-like heating element 310,or heater, which can include a first side edge 301 and a second sideedge 302. According to preferred embodiments of the present invention,heating element 310 comprises a conductive fabric or a fabricincorporating closely spaced conductive elements such that heatingelement 310 has a substantially uniform watt density output, preferablyless than approximately 0.5 watts/sq. inch, and more preferably betweenapproximately 0.2 and approximately 0.4 watts/sq. inch, across a surfacearea, of one or both sides 313, 314 (FIG. 2B).

Some examples of conductive fabrics which may be employed by embodimentsof the present invention include, without limitation, carbon fiberfabrics, fabrics made from carbonized fibers, conductive films, or wovenor non-woven non-conductive fabric or film substrates coated with aconductive material, for example, polypyrrole, carbonized ink, ormetalized ink. In many embodiments, the conductive fabric is a polymericfabric coated with a conductive polymeric material such as polypyrrole.In addition, the flexible heating element 310 may be made from a matrixof electrically resistant wire or metal traces attached to a fibrous orfilm material layer.

FIG. 2A further illustrates subassembly 300 including two bus bars 315coupled to heating element 310 for powering heating element 310. Eachbar 315 is shown extending between first and second side edges 301, 302.With reference to FIG. 2B, according to some embodiments, bus bars 315are coupled to heating element 310 by a stitched coupling 345 (e.g.,formed with conductive thread such as silver-coated polyester or nylonthread (Marktek Inc., Chesterfield, Mo.)).

As shown, insulation is provided between the bus bars 315 and theheating element 310. FIG. 2B illustrates subassembly 300 whereininsulating members 318 (e.g., fiberglass material strips having anoptional PTFE coating and a thickness of approximately 0.003 inch)extend between bus bars 315 and heating element 310 at each stitchedcoupling 345, so that electrical contact points between bars 315 andheating element 310 are solely defined by the conductive thread ofstitched couplings 345. Alternatively, the electrical insulationmaterial layer could be made of polymeric film, a polymeric filmreinforced with a fibrous material, a cellulose material, a glassfibrous material, rubber sheeting, polymeric or rubber coated fabric orwoven materials or any other suitable electrically insulating material.

Each of the conductive thread stitches of coupling 345 can maintain astable and constant contact with bus bar 315 on one side and heatingelement 310 on the other side of insulating member 318. The stitchesproduce a stable contact in the face of any degree of flexion, so thatthe potential problem of intermittent contact between bus bar 315 andheating element 310 (that could arise for the embodiment shown in FIG.2B, where bus bar 315 is in physical contact with heating element 310)can be avoided. The stitches are the only electrical connection betweenbus bar 315 and heating element 310, but, since the conductive threadhas a much lower electrical resistance than the conductive fabric ofheating element 310, the thread does not heat under normal conditions.

In addition to heating blanket applications described herein, such adesign for providing for a uniform and stable conductive interfacebetween a bus bar and a conductive fabric heating element material canbe used in other applications. For example, such a design can improvethe conductive interface between a bus bar or electrode and a conductivefabric in non-flexible heating elements, in electronic shielding, inradar shielding and other applications of conductive fabrics.

In some preferred embodiments, coupling 345 includes two or more rows ofstitches for added security and stability. However, due to the flexiblenature of blanket subassembly 300, the thread of stitched couplings 345may undergo significant stresses. These stresses, over time and withmultiple uses of a blanket containing subassembly 300, could lead to oneor more fractures along the length of stitched coupling 345. Such afracture, in other designs, could also result in intermittent contactpoints, between bus bar 315 and heating element 310, that could lead toa thermal breakdown of heating element 310 along bus bar. But, if such afracture were to occur in the embodiment of FIG. 2B, insulating member318 may prevent a thermal breakdown of heating element 310, so that onlythe conductive thread of stitched coupling 345 melts down along bus bar315. According to some preferred embodiments, more than two rows ofstitches are applied to each bus bar 315 for added safety and stabilityof the bus bar/heating element interface.

Alternative threads or yarns employed by embodiments of the presentinvention may be made of other polymeric or natural fibers coated withother electrically conductive materials. In addition, nickel, gold,platinum and various conductive polymers can be used to make conductivethreads. Metal threads such as stainless steel, copper or nickel couldalso be used for this application.

According to an exemplary embodiment, bars 315 are comprised offlattened tubes of braided wires, such as are known to those skilled inthe art (e.g., a flat braided silver coated copper wire) and may thusaccommodate the thread extending therethrough, passing through openingsbetween the braided wires thereof. In addition such bars are flexible toenhance the flexibility of blanket subassembly 300. According toalternate embodiments, bus bars 315 can be a conductive foil or wire,flattened braided wires not formed in tubes, an embroidery of conductivethread, or a printing of conductive ink. Preferably, bus bars 315 areeach a flat braided silver-coated copper wire material, since a silvercoating has shown superior durability with repeated flexion, as comparedto tin-coated wire, for example, and may be less susceptible tooxidative interaction with a polypyrrole coating of heating element 310according to an embodiment described below. Additionally, an oxidativepotential, related to dissimilar metals in contact with one another isreduced if a silver-coated thread is used for stitched coupling 345 of asilver-coated bus bar 315.

According to an exemplary embodiment, a conductive fabric comprisingheating element 310 comprises a non-woven polyester having a basisweight of approximately 170 g/m2 and being 100% coated with polypyrrole(available from Eeonyx Inc., Pinole, CA). The coated fabric has anaverage resistance (e.g., determined with a four point probemeasurement) of approximately 15 ohms per square inch. This averageresistance is suitable to produce the preferred watt density of 0.2 to0.4 watts/sq. in. for surface areas of heating element 310 having awidth, between bus bars 315, in the neighborhood of about 19 to 28inches, when powered at about 48 volts. In some embodiments, the basisweight of the non-woven polyester may be chosen in the range ofapproximately 80-180 g/m2. However, other basis weights may beengineered to operate adequately are therefore within the scope ofembodiments of the invention.

A resistance of such a conductive fabric may be tailored for differentwidths between bus bars (wider requiring a lower resistance and narrowerrequiring a higher resistance) by increasing or decreasing a surfacearea of the fabric that can receive the conductive coating. In someinstances, this can be achieved by increasing or decreasing the basisweight of the nonwoven. Resistance over the surface area of theconductive fabrics is generally uniform in many embodiments of thepresent invention. However, the resistance over different portions ofthe surface area of conductive fabrics such as these may vary (e.g., dueto (a) variation in a thickness of a conductive coating, (b) variationwithin the conductive coating itself, (c) variation in effective surfacearea of the substrate which is available to receive the conductivecoating, or (d) variation in the density of the substrate itself). Localsurface resistance across a heating element, for example heating element310, is directly related to heat generation according to the followingrelationship:

Q(Joules)=I2(Amps)×R(Ohms)

Variability in resistance thus translates into variability in heatgeneration, which can ultimately manifest as a variation in temperature.

According to preferred embodiments of the present invention, which areemployed to warm patients undergoing surgery, precise temperaturecontrol is desirable. Means for determining heating elementtemperatures, which average out temperature variability caused byresistance variability across a surface of the heating element, aredescribed below in conjunction with FIG. 3A.

Referring again to FIGS. 2A-2B, the flexibility of blanket subassembly300 can allow blanket subassembly 300 to conform to the contours of abody (e.g., all or a portion of a patient undergoing surgery). Thisflexibility can be provided primarily by flexible heating element 310and can be optionally enhanced by the incorporation of flexible busbars. Conforming to the contours of a patient's body is preferable tosimply bridging across high spots of the body. Such conformance mayoptimize a conductive heat transfer from heating element 310 to asurface of the body.

The uniform watt-density output across the surface areas of preferredembodiments of heating element 310 translates into generally uniformheating of the surface areas, but not necessarily a uniform temperature.For example, at locations of heating element 310 which are in conductivecontact with a body acting as a heat sink, the heat is efficiently drawnaway from heating element 310 and into the body (e.g., by blood flow).At the same time, at those locations where heating element 310 does notcome into conductive contact with the body, an insulating air gap existsbetween the body and those portions, so that the heat is not drawn offthose portions as easily. Therefore, those portions of heating element310 not in conductive contact with the body will gain in temperature,since heat is not transferred as efficiently from these portions as fromthose in conductive contact with the body. The ‘non-contacting’ portionswill reach a higher equilibrium temperature than that of the‘contacting’ portions, when the radiant and convective heat loss equalthe constant heat production through heating element 310. Since the heatgeneration is generally uniform, the heat flux to the patient will alsobe generally uniform. However, at the non-contacting locations, thetemperature is higher to achieve the same flux as the contactingportions. Some of the extra heat from the higher temperatures at thenon-contacting portions can therefore be dissipated out the back of thepad instead of into the patient.

Although radiant and convective heat transfer are more efficient athigher heater temperatures, the laws of thermodynamics dictate that aslong as there is a uniform watt-density of heat production, even at thehigher temperature, the radiant and convective heat transfer from ablanket of this construction will result in a generally uniform heatflux from the blanket. Therefore, by controlling the ‘contacting’portions to a safe temperature (e.g., via a temperature sensor assembly321 coupled to heating element 310 in a location where heating element310 will be in conductive contact with the body), the ‘non-contacting’portions, will also be operating at a safe temperature because of theless efficient radiant and convective heat transfer.

According to preferred embodiments, heating element 310 comprises aconductive fabric having a relatively small thermal mass. When a portionof such a heating element that is operating at the higher temperature istouched, suddenly converting a ‘non-contacting’ portion into a‘contacting’ portion, that portion will cool almost instantly to thelower operating temperature.

FIGS. 3A-3B show a heating element assembly 350 similar to the heatingelement assembly 350 of FIG. 1. Referring again to FIGS. 3A-3B, theheating element assembly can include a temperature sensor assembly 321.As shown, the temperature sensor assembly 321 is coupled to heatingelement 310 at a location where heating element 310 would come intoconductive contact with the patient. This can assist in maintaining asafe temperature distribution across heating element 310. The moreconstant the temperature information, the more the temperaturecontroller can rely on it in controlling the heater temperature. In someembodiments, the temperature sensor assembly 321 can even be providedseparately from the heating blanket.

According to embodiments of the present invention, zones of heatingelement 310 may be differentiated according to whether or not portionsof heating element 310 are in conductive contact with a body (e.g., apatient undergoing surgery). In some embodiments, the thresholdtemperature is between 37 and 43° C. In one particular embodiment, thethreshold temperature is 43° C. A temperature of 43° C. has been shownto provide beneficial warming to a patient without providing excessiveheat. In the case of conductive heating, gentle external pressure may beapplied to a heating blanket including heating element 310. Suchpressure conforms heating element 310 into better conductive contactwith the patient to improve heat transfer. However, if excessivepressure is applied, the blood flow to that skin may be reduced at thesame time that the heat transfer is improved and this combination ofheat and pressure to the skin can be dangerous. It is well known thatpatients with poor perfusion should not have prolonged contact withtemperatures in excess of approximately 42° C. Several studies show 42°C. to be the highest skin temperature that cannot cause thermal damageto normally perfused skin, even with prolonged exposure. (Stoll &Greene, Relationship Between Pain and Tissue Damage Due to ThermalRadiation. J. Applied Physiology 14(3):373-382. 1959; and Moritz andHenriques, Studies of Thermal Injury: The Relative Importance of Timeand Surface Temperature in the Causation of Cutaneous Burns. Am. J.Pathology 23:695-720, 1947). Thus, according to certain embodiments ofthe present invention, the portion of heating element 310 that is inconductive contact with the patient is controlled to approximately 43°C. in order to achieve a temperature of about 41-42° C. on a surface ofa heating blanket cover that surrounds heating element 310 (e.g., shell105 of FIG. 1).

FIG. 3B illustrates the temperature sensor assembly 321 assembled onside 314 of the heating element 310. As shown, the heating element 310is overlaid on both sides 313, 314 with an electrically insulating layer330. The electrically insulating layer 330 is preferably formed of aflexible non-woven very low loft fibrous material (e.g., 1.5ounces-per-square-yard nylon), which is preferably laminated to sides313, 314 with a hotmelt laminating adhesive. In some embodiments, theadhesive is applied over the entire interfaces between insulating layer330 and heating element 310. Other examples of suitable materials forinsulating layer 330 include, without limitation, polymeric foam, awoven fabric, such as cotton or fiberglass, and a relatively thinplastic film, cotton, and a non-flammable material, such as fiberglassor treated cotton. According to preferred embodiments, overlaidinsulating layers 330 prevent electrical shorting of one portion ofheating element 310 with another portion of heating element 310 ifheating element 310 is folded over onto itself. Many such embodimentsprevent electrical shorting without compromising the flexibility ofheating assembly 350. Heating element assembly 350 may be powered by arelatively low voltage (approximately 48V). Insulating layers 330 mayeven be porous in nature to further maintain the desired flexibility ofassembly 350.

As shown in FIG. 3A, an assembly of leads 305, 306 and junctions 355 canconnect the bus bars 315 and the temperature sensor assembly 321 to anelectrical connector housing 325. Leads 305 couple the connector housing325 to bus bars 315 at junctions 355. Lead 306 couples the temperaturesensor assembly 321 to the connector housing 325. In many embodiments,leads 305, 306 extend over any insulating layer (e.g., 330 in FIG. 3B)and into the electrical connector housing 325. As is noted above (seediscussion in connection with FIG. 1) and discussed in greater detailbelow (see discussion in connection with FIG. 4A), electrical connectorhousing 325 can contain a connector plug 323.

Returning now to FIG. 3B, the illustrative temperature sensor assembly321 will be described in greater detail. The temperature sensor assembly321 can include a temperature sensor 351 (e.g., a surface mount chipthermistor (such as a Panasonic ERT-J1VG103FA: 10K, 1% chip thermistor))soldered to an etched metal foil. In many embodiments, a substrate 331(e.g., of polyimide (Kapton)) surrounds the temperature sensor 351. Aheat spreader 332 (e.g., a copper or aluminum foil) can be mounted to anopposite side of substrate 331 (e.g., being bonded with a pressuresensitive adhesive). Substrate 331 can be relatively thin (e.g., about0.0005-inch thick) so that heat transfer between heat spreader 332 andsensor is not significantly impeded.

In some embodiments, the temperature sensor 351 is positioned such thatthe regions surrounding sensor 351 will be in conductive contact withthe body when a heating blanket is placed over a body. As previouslydescribed, in many instances, it is desirable that a temperature ofapproximately 43° C. be maintained over a surface of heating element 310which is in conductive contact with a body of a patient undergoingsurgery. An additional alternate embodiment is contemplated in which anarray of temperature sensors are positioned over the surface of heatingelement 310, being spaced apart to collect temperature readings. In somesuch embodiments, the collected temperatures can be averaged to accountfor resistance variance.

FIGS. 4A-4B show a heating element assembly 350 that may be incorporatedinto a heating blanket (e.g., heating blanket 100 of FIG. 1). As shown,the heating element assembly 350 includes heating element 310 overlaidwith electrical insulation 330 on both sides 313, 314 and thermalinsulation layer 311 extending over the top side 314 thereof (dashedlines show leads and sensor assembly beneath layer 311).

A heating blanket may include a layer of thermal insulation 311extending over a top side (corresponding to side 314 of heating element310 as shown in FIG. 2B) of heating assembly 350 as discussed above.According to the illustrated embodiment, layer 311 is inserted beneath aportion of each insulating member 318. The insulating members 318 havebeen folded over the respective bus bar 315 (e.g., as illustrated byarrow B in FIG. 2B), and then held in place by a respective row ofnon-conductive stitching 347 that extends through insulating member 318,layer 311 and heating element 310. Although not shown, it should beappreciated that layer 311 may further extend over bus bars 315.Although insulating layer 330 is shown extending beneath layer 311 onside 314 of heating element 310, according to alternate embodiments,layer 311 independently performs as a thermal and electrical insulationso that insulating layer 330 is not required on side 314 of heatingelement 310. FIG. 4A further illustrates, with longitudinally extendingdashed lines, a plurality of optional slits 303 in layer 311, which mayextend partially or completely through layer 311, in order to increasethe flexibility of assembly 350. Such slits are desirable if a thicknessor density of layer 311 is such that it prevents the heating blanketfrom draping effectively about a patient. The optional slits arepreferably formed, for example, extending only partially through layer311 starting from an upper surface thereof, to allow bending of theheating blanket about a patient and to prevent bending of the heatingblanket in the opposition direction.

Returning now to FIG. 3A, to be referenced in conjunction with FIGS. 1and 4A, connector housing 325 and connector plug 323 will be describedin greater detail. According to certain embodiments, housing 325 is aninjection molded thermoplastic (e.g., PVC) and may be coupled toassembly 350 by being stitched into place, over insulating layer 330.FIG. 3A shows housing 325 including a flange 353 through which suchstitching can extend.

Referring to FIGS. 1 and 4A, in some embodiments, a surface of flange353 of housing 325 protrudes through a hole formed in thermal insulatinglayer 311 so that a seal may be formed (e.g., by adhesive bonding and/orwelding, such as heat sealing) between an inner surface of shell 105 andsurface 352. According to one embodiment, wherein housing 325 isinjection molded PVC and the inner surface of shell 105 is likewise PVC,housing 325 is sealed to shell 105 via a solvent bond. It may beappreciated that the location of the connector plug 323 is suitable tokeep the corresponding connector cord well away from the surgical field.In embodiments in which the inner surface of shell 105 is coated withpolyurethane and the housing 325 is injection molded PVC, anintermediate adhesive can be used to allow for a heat seal connection(e.g., a solvent bond adhesive can be applied to the housing 325, andthe polyurethane film can be heat sealed to the exposed adhesive).

FIGS. 4A-4B further illustrate a pair of securing strips 317, eachextending laterally from and alongside respective lateral portions ofheating element 310, parallel to bus bars 315, and each coupled to side313 of heating element 310 by the respective row of non-conductivestitching 347. Another pair of securing strips 371 is shown in FIG. 4A,each strip 371 extending longitudinally from and alongside respectiveside edges 301, 302 of heating element 310 and being coupled thereto bya respective row of non-conductive stitching 354. Strips 371 may extendover layer 311 or beneath heating element 310. As shown, strips 317preferably extend over conductive stitching of stitched coupling 345 onside 313 of heating element 310. The strips 317 can provide a layer ofinsulation that can prevent shorting between portions of side 313 ofheating element 310 if heating element 310 were to fold over on itselfalong rows of conductive stitching of stitched coupling 345 that couplebus bars 315 to heating element 310. In some embodiments, strips 317 mayalternately extend over insulating member 318 on the opposite side ofheating element 310. According to the illustrated embodiment, securingstrips 317 and 371 are made of a polymer material (e.g., PVC). They maybe heat sealed between the sheets of shell (105 of FIG. 1) incorresponding areas of the heat seal zone in order to secure heatingelement assembly 350 within a corresponding gap between the two sheetsof shell (105 of FIG. 1). According to an alternate embodiment, forexample, shown by dashed lines in FIGS. 2A and 4B, heating element 310extends laterally out from each bus bar 315 to a securing edge 327,which may include one or more slots or holes 307 extending therethroughso that inner surfaces of sheets of shell (105 of FIG. 1) can contactone another to be sealed together and thereby hold edges 327.

Referring to FIG. 1, connector plug 323 can protrude from shell 105 ofthe heating blanket 100. An extension cable may couple the heatingelement assembly 350 to a console 60. The console 60 includes a shut-offtimer 30 and a power source 50 each coupled to a control system (orcontroller) 40. The shut-off timer 30 can be operatively coupled to thecontrol system 40, meaning that the shut-off timer 30 can be integratedinto the control system 40, the shut-off timer 30 can be a separatecomponent, or the shut-off timer 30 and the control system 40 can haveany other suitable functional relationship. The temperature sensorassembly 321 can be configured to provide temperature information to thecontrol system 40, which may act as a temperature controller. Thecontroller may function to interrupt such power supply (e.g., in anover-temperature condition) or to modify the duty cycle to control theheating element temperature.

The power source 50 and power type can be any type known in the art. Incertain embodiments, the power source 50 supplies a straight-line DCvoltage to the control system 40, and the control system 40 provides apulse-width-modulated voltage (e.g., at a 75% duty cycle) to the heatingelement assembly 350. Of course, other duty cycles and/or voltage levelscan be used based on the design of the blanket and its heating elementin order to achieve a desired threshold temperature in a reasonableamount of time. Too high of voltage or duty cycle, while decreasing thetime to reach the desired temperature threshold, may increase the amountof temperature overshoot before the control system reduces or shuts offpower. Moreover, in the case of temperature sensor failure, thermalrunaway presents a greater concern with relatively higher voltage orduty cycle settings. Too low of a voltage or duty cycle may causeunreasonably long warm-up times.

As discussed above, warming blankets in accordance with embodiments ofthe invention include or make use of a shell or covering, such as shell105 shown in FIG. 1. Several embodiments of such shells will now bedescribed in greater detail, although it should be understood that theseembodiments are for illustrative purposes only.

FIG. 5A is a cross-section of a shell 500 containing a heating element502 in accordance with some embodiments of the invention. The shell 500can include a top sheet 504 and a bottom sheet 506 that are welded orcoupled at one or more locations in order to define a pocket or pouch508 that can enclose the heating element 502. Any type of suitable weldmay be used, such as heat welding (heat bonding), RF welding, ultrasonicwelding, etc., depending on the type of materials used in sheets 504,506. Each sheet 504 and 506 can comprise a flexible, substantiallywater-resistant material and include the ability to be welded together.In some embodiments, the water-resistant material includes a singlelayer, and in some embodiments, sheets are comprised of a laminate oftwo or more layers. For instance, in some embodiments one or both ofsheets 504, 506 are comprised of a single layer of polyvinyl chloride(PVC). In such embodiments where PVC is used, high frequency or RFwelding (RF heat sealing) may be used to bond the sheets 504, 506together. PVC sheets also provide a water-resistant material in order toprotect the heating element 502 from fluids to which the heating blanketis exposed.

In some embodiments, one or both of sheets 504, 506 include respectivestrengthening layers 510, 512 that provide strength and color to theshell 500. For example, the strengthening layers 510, 512 can be afibrous material such as woven nylon. It will be appreciated that othermaterials can also be used for this layer.

With further reference to FIG. 5A, sheets 504, 506 can each also includea second layer 514, 516 located along an inside surface of the sheets504, 506. These second layers can in some embodiments provide awater-resistant layer in order to protect the heating element 502 fromfluids to which the heating blanket is exposed. For example, the secondlayers 514, 516 can be a polymeric film attached to the strengtheninglayer. In some embodiments, the second layers 514, 516 are preferablypolymeric film layers that are a durable and made of a weldablematerial, such as urethane or vinyl, which can be laminated or extrusioncoated on to the strengthening layers 510, 512 and the second layers514, 516 may be welded together via heating bonding along the bondingpoints.

In some embodiments, one or both of sheets 504, 506 include a thirdlayer laminated to their respective outer surfaces. The third layer, insome embodiments, is a polymeric layer, which may or may not be the samematerial as second layers 514, 516 in some embodiments. For example, thethird layer can comprise a polymeric layer that can substantially sealone or both of the strengthening layers so that it cannot besubstantially wetted. In some embodiments, the third layer may also besomewhat tacky so that it prevents the blanket from slipping whenapplied over a patient. The third layer may also comprise a materialwith the ability to limit and/or prevent iodine and cleaning solutionsfrom staining the blanket. Examples of materials that could serve thispurpose include vinyl and silicone.

With further reference to FIG. 5A, top sheet 504 and bottom sheet 506can be positioned on opposing sides of heating element 502 to envelopethe heating element. Although descriptive terms “top” and “bottom” areused herein, it will be appreciated that in some embodiments, the sheets504 and 506 may be identical and that either sheet may be referred to as“top” or “bottom.” As shown in the embodiment of FIG. 5A, the sheets arepositioned so that the weldable layers 514, 516 of each sheet opposeeach other.

FIG. 5B is a top plan view of the heating blanket depicted in FIG. 5A.In some embodiments, the sheets 504, 506 are sized to completely coverthe heating element 502, and can extend beyond all edges (e.g., top,bottom, right and left side edges in FIG. 5B) of the heating element502. In some embodiments, the heating element 502 is substantiallyhermetically sealed into the shell 500 formed by the two sheets 504,506. As shown in the embodiment of FIGS. 5A and 5B, the sheets 504, 506are coupled together along two welds. A first weld 518 can extend abouta perimeter 520 of the heating element 502, thus surrounding the entireperiphery of the heating element. A second weld 522 can extend about aperimeter edge 524 of the sheets 504, 506, thus sealing the periphery ofthe sheets together. In some embodiments, the space 526 between thefirst weld 518 and the second weld 522 may be totally or partiallywelded together. In alternate embodiments, the space 526 between thewelds may contain other structural components of the blanket aspreviously described and further discussed below. For example, the space526 can enclose weighting members, the added weight of which helpsretain the blanket in position and against the patient.

The weld used in some embodiments to create a substantially hermeticallysealed shell for protecting the heating element provides a number ofadvantages over traditional bonding mechanisms such as sewing, stitches,rivets or grommets that create or reinforce a seal. In certainembodiments of those that employ a heat sealed shell, the externalsurface of the substantially hermetically sealed shell is not puncturedby needle holes, sewing, stitching, rivets, grommets or other fasteners.These traditional fasteners create holes and can accumulate contaminantsfrom blood and body fluids. These holes, crevasses, and fibrousmaterials such as thread are difficult or even impossible to clean withstandard cleaning methods and solutions. Exemplary heating blanketsdescribed herein can advantageously have a smooth, non-violated shell,without external attachments or physical places to trap contaminants,thus providing a readily and thoroughly cleanable heating blanket insome embodiments. As will be appreciated, the welded construction usedin some embodiments can also facilitate a variety of features that wouldotherwise require traditional fasteners such as sewing, stitching,riveting, grommets or snaps.

In some embodiments, portions of the shell extending beyond theperimeter of the heating element can form non-heated edge flaps of theheating blanket, such as those described above. Exemplary non-heatededge flaps can preferably extend from 1 inch to 24 inches away from theperimeter of the heating element, although it will be appreciated thatany suitable length of extension is possible. The non-heated edge flapscan be used to create a cocoon-like space that traps the heat from theheater in a space around the patient. For example, in alternativeembodiments, the edges 112, 114, 116, and 118 of the heating blanketdepicted in FIG. 1 can include non-heated edge flaps instead of lateralportions of the heating element. The non-heated edge flaps can thuscreate a thermal barrier between the heater edge and the operating tableor bed. In some embodiments, the two sheets of the non-heated edge flapsmay be partially or completely welded together between the first weldabout the perimeter of the heating element and the second weld about theperimeter of the warming blanket. With reference to FIG. 6, inembodiments with a partial weld, the non-welded area may include an airpocket 530. Air can be introduced into the space 526 between the firstweld 518 and the second weld 522. Embodiments with such an air pocket530 can thus provide a thermal barrier that further limits the escape ofheat from the space around the patient.

With reference to FIG. 7A, some exemplary heating blankets can includeone or more straps 532 extending from the blanket for securing theblanket in place over the patient. In some embodiments, the straps 532are preferably of the same material and contiguous with the sheetsmaking up the shell and protrude from the edges of the sheets such thatthere is no seam joining the straps 532 with the sheets. In someembodiments, holes 534 can be punched in the straps 532 to facilitatebuckling the straps (e.g., to another blanket strap extending from adifferent edge of the blanket, to a protuberance extending from theblanket, etc.), hanging the warming blanket, or other common uses. Withreference to FIG. 7B, some embodiments can include a reinforcing layer536 positioned between the sheets 504, 506 before they are welded inorder to reinforce the straps 532. For example, the reinforcing layercan in some embodiments comprise a plastic film such as a urethane film.The reinforcing layer may be formed in addition to strengthening layerof sheets 504, 506 described above. Alternatively, the reinforcing layercould be formed by the inclusion of the strengthening layer on one orboth of sheets 504, 506 at the strap locations shown in FIG. 7A. As willbe appreciated, the straps 532 are provided with the warming blanketwithout the addition of sewing, stitching, grommets or other traditionalfasteners, thus providing the advantages previously discussed.

As previously discussed with reference to at least FIGS. 2A, 4A and 4B,securing strips 317, 371 or securing edges 327 can be provided in someembodiments to facilitate securing the heating element to the shell.With reference to FIG. 8, an exemplary securing strip 540 can comprise aweldable plastic film, for example, a urethane film. A first end 542 ofthe securing strip 540 can be attached to the heating element 502, forexample by sewing. A second end 544 of the securing strip 540 (orsecuring edge according to alternate embodiments) can be placed betweenthe two sheets 504, 506 and incorporated into the welds between the twosheets. Thus the heater is held in an extended position within theshell, without using stitches, sewing, rivets or grommets that wouldpierce the flexible material sheets and make the shell difficult toclean.

With reference to FIGS. 9A-9B, some exemplary shells provide reinforcedhanger points 550 without the use of grommets or another similarmechanism for reinforcement. As shown, a reinforcing layer 552 extendsbetween the sheets 504, 506 where they are welded at one end about theperimeter of the heating element 502. The reinforcing layer 552 may beformed in addition to strengthening layer of sheets 504, 506. In someembodiments more than one reinforcing layer may be utilized, forexample, on opposing ends of the shell 500 or one layer integrated intoone of both of sheets 504, 506. The reinforcing layer 552 can in someembodiments comprise one or more pieces of thermally bondable plasticfilm, for example a urethane film. The reinforcing layer 552 isincorporated into a weld 554 that may extend from near the perimeter ofthe heater to near the perimeter of the sheets. One or more holes can bepunched through both sheets and through the reinforcing layer 552 tocreate a hanging point 550. The exemplary reinforcing layer 552reinforces the hanging point 550 without the need for additionalgrommets that would make the blanket more difficult to clean.

With reference to FIGS. 10A-10B, exemplary shells are shown with anincorporated anchor point 560. As shown, the anchor point 560 can insome embodiments be a “ball-shaped” or a “mushroom-shaped” protuberancewhich can serve as an attachment post on which a strap with holes in itmay be secured, for example, the straps of FIGS. 7A-7B. The anchor point560 can be made of plastic or some other material such as metal. Asshown in FIGS. 10A-10B, the anchor point 560 can be molded or otherwiseattached to an anchoring layer 562, which in some embodiments comprisesa flat piece of thermally bondable plastic material, such as, forexample, a urethane material. The anchoring layer 562 can be placedbetween the two sheets 504, 506 about the perimeter of the heatingelement 502 and the anchor point 560 can extend from the edges of thesheets as in FIG. 10B or through a hole 564 made in one of the sheets asin FIG. 10A. The sheets 504, 506 can be welded to the anchoring layer562 to anchor the anchoring layer 562 between the sheets and also toseal the cut edge of the hole 564 or edge of the sheets.

In some embodiments, a piece of ribbing or piping can be molded to theedge of an anchoring layer similar to that shown in FIG. 10B. Theanchoring layer can then be placed between the two sheets at their edgessuch that the ribbing or piping protrudes beyond the edges of thesheets. Exemplary ribbing or piping may be plastic or another suitablematerial such that the ribbing or piping advantageously seals the edgesof the shell and creates a soft edge to the warming blanket. Portions ofthe ribbing or piping may include the anchor point 560.

With reference to FIG. 11, in some embodiments, a warming blanket can besecured to a patient with one or more magnets and/or ferrous metalpieces. FIG. 11 shows two opposing ends 570, 572 of a single shell 500and warming blanket configured in a loop according to some embodiments.As shown, a magnet 574 can be fixed in position between sheets 504, 506at end 570 via appropriately placed welds of sheets 504, 506.Alternately a ferrous metal piece 576 or another magnet can be fixed inposition between sheets 506, 504 at end 572 in the same manner as magnet574. The magnet 574 is placed in a position to mate with ferrous metalpiece 576, securing the blanket in place. The metal piece 576 and themagnet 574 are both contained between the sheets and therefore do notcomplicate the cleaning of the warming blanket.

In the foregoing detailed description, the invention has been describedwith reference to specific embodiments. However, it may be appreciatedthat various modifications and changes can be made without departingfrom the scope of the invention as set forth in the appended claims.Although embodiments of the invention are described in the context of ahospital operating room, it is contemplated that some embodiments of theinvention may be used in other environments. Those embodiments of thepresent invention, which are not intended for use in an operatingenvironment and need not meet stringent FDA requirements for repeatedused in an operating environment, need not including particular featuresdescribed herein, for example, related to precise temperature control.Thus, some of the features of preferred embodiments described herein arenot necessarily included in preferred embodiments of the invention whichare intended for alternative uses.

1. An electric heating blanket, comprising: a flexible sheet-likeheating element including an upper edge, a lower edge, and at least twoside edges; a shell covering the heating element and comprising at leasttwo sheets of flexible material; and a weld coupling the two sheets offlexible material together about the edges of the heating element. 2.The electric heating blanket of claim 1, wherein the weld is one of a RFweld, ultrasonic weld, or a heat bond.
 3. The electric heating blanketof claim 1, wherein the two sheets are comprise PVC.
 4. The electricheating blanket of claim 1, wherein each sheet comprises a strengtheninglayer and a second layer.
 5. The electric heating blanket of claim 1,wherein the strengthening layer comprises woven nylon and the secondlayer comprises a water-resistant material that facilitates the thermalbond.
 6. The electric heating blanket of claim 5, wherein each sheetfurther comprises a third layer on an outside surface of the sheet, thethird layer including a water-resistant material.
 7. The electricheating blanket of claim 6, wherein the third layer comprises ananti-slip surface.
 8. The electric heating blanket of claim 1, furthercomprising at least one air pocket incorporated into the thermal bondcoupling the two sheets.
 9. The electric heating blanket of claim 1,wherein the sheets further comprise at least one strap.
 10. The electricheating blanket of claim 9, wherein the at least one strap comprises areinforcing layer.
 11. The electric heating blanket of claim 10, whereinthe at least one strap is integrally formed with at least one of thesheets.
 12. The electric heating blanket of claim 10, further includingan attachment post on which the strap may be secured.
 13. The electricheating blanket of claim 12, wherein the attachment post is integrallyformed with an anchoring layer that is thermally bonded between thesheets.
 14. The electric heating blanket of claim 1, further comprisingat least one securing strip coupled to the heating element, the at leastone securing strip being coupled to the shell by the thermal bond. 15.The electric heating blanket of claim 1, further comprising areinforcing layer between the sheets and incorporated into the thermalbond, and at least one hanger point through the sheets and thereinforcing layer.
 16. The electric heating blanket of claim 1, furthercomprising an anchor point coupled to an anchoring layer, wherein theanchoring layer is incorporated into the thermal bond.
 17. The electricheating blanket of claim 1, further comprising at least one magnetlocated within the thermal bond coupling the sheets.
 18. An electricheating blanket, comprising: a flexible sheet-like heating element; ashell covering the heating element and comprising at least two sheets offlexible material; and one or more welds coupling the two sheets offlexible material together about the edges of the two sheets tohermetically seal the heating element therebetween.
 19. The electricheating blanket of claim 18, wherein the heating element is held inposition between the two sheets without using connectors that pierce thetwo sheets.
 20. The electric heating blanket of claim 18, wherein thetwo sheets include a hole passing through the one or more thermal bondsto form a hanging point for the electric heating blanket.
 21. Theelectric heating blanket of claim 18, wherein ribbing or piping, forminga soft peripheral edge to the electric heating blanket, extends beyondthe edges of the two sheets and is held in place via the one or morewelds.
 22. An electric heating blanket, comprising: a flexiblesheet-like heating element; a shell covering the heating element andcomprising at least two sheets of flexible material; a first weldcoupling the two sheets of flexible material together about an outerperiphery of the flexible heating element to hermetically seal theheating element therebetween; and a second weld coupling the two sheetsof flexible material together about a periphery of the sheets to sealthe peripheries of the two sheets together.
 23. The electric heatingblanket of claim 22, wherein an air pocket is created between the twosheets of flexible material and between the first and second thermalwelds.
 24. The electric heating blanket of claim 22, wherein magnets areretained in place between the two sheets of flexible material andbetween the first and second welds, the magnets being usable to hold theedges of the blanket together, whereby the blanket may be wrapped abouta patient and the edges may be held together via the magnets.